See the recent post ‘Dodge Intrepid 2001 – Infinity I Sound System Flashing Lights Problem’ if you haven't already (I can’t post the URL because I don’t have 5 posts on the forum yet – sorry). We have the same car. Have you been able to determine your Radio/Cass unit’s Sales Code? It should be printed on the display’s face-plate under the Clock Setting (H/M) recessed buttons - mine's there and it’s RBB for the Infinity I system.
I'm assuming you've checked the 'Radio' fuse on the Junction Block on the left-hand side of the instrument panel. If not, the removable panel has the layout on it. I see you have 'nothing' on the Radio/Cass unit. Do the lights on your CD unit come on or are they out as well?
I've owned the car since new and have had only a few electrical issues. I was worried about the high number of 'Control Modules' the car has and it's PCI Communications Bus/Protocol complexity but after 8+ years I have to say I'm pretty satisfied.
The Transmission Control Module (TCM) was the first problem and that required the dealer - a big 'ouch!' if you're not under warranty (as I was by only 19 miles!). After that I had problems with the Stereo (mentioned in the link above), the Factory Anti-Theft System (Door Cylinder Lock Switches and a break in the Trunk Lock Cylinder Knockout Switch wiring) and the passenger Door Motor/Ajar Switch/Latch assembly - all of which I was able to fix at home w/parts.
One thing I will say is that the 2001 DamilerChrysler Corp. Factory Service Manual (FSM) for the car has the BEST electrical schematics I've seen. I've found some errors (some radiator mounted fan relays missing in the A/C circuits for example) but then I don't subscribe to Technical Service Bulletin Updates, so these issues may have been corrected in future editions. I always make the FSM a part of the deal for any new car I buy and DCC has definitely beaten what I've gotten from GM and Porsche with regards to electrics. GM wins in the 'mechanical' arena though - super detail.
Chiefload's 'how to' is spot on but I would suggest you disconnect you Negative Battery Terminal (at its remote location) first! I'd also add four things to his sixth step for your system (Infinity):
1) When you withdraw the Radio/Cass unit from the dash do this slowly - there's plenty of cable but it tends to 'hang-up' if you don't fiddle with it and you don't want to hurt the harness or stress the connectors. You’ll probably need to get your hand back in there once there’s room and ‘help’ things along.
2) You should also have a single wire PCI Bus interface connection to remove.
3) You should also have a braided copper wire ground strap to remove which requires a wrench. Save the ground strap's 'bolt' as it doesn't come with the AER replacement unit.
4) You will also need to remove the CD Unit's connection - it's of DIN design and, while tight, comes out with a firm, straight pull out from the back of the Radio/Cass unit.
As Chiefload states, the install is the reverse of all of this. Make sure you 'slowly' feed the various cables back into the dash to insure you don’t bind/stress anything. Re-connect the Batt's Ground cable and that should be all you need.
The Infinity I system I have has been one sweet system and I'm glad to have it working again. Hope you're in the same position soon!